Exhaust gas generated by combustion of fossil fuels in furnaces, ovens, and engines, for example, contains nitrogen oxides (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO). Automobile gasoline engines utilize various pollution-control after treatment devices such as, for example, a three-way catalyst converter to reduce and oxidize NOx, CO, and HC. The NOx reduction is accomplished by using ammonia gas (NH3) supplied by a urea tank, or by using HC and CO, which is generated by running the engine temporarily in rich conditions. The overall reaction for converting urea to ammonia is:NH2CONH2+H2O(steam)→2NH3+CO2+H2O.The product gas is a mixture of ammonia gas, carbon dioxide (CO2), and water vapor. In order for urea-based catalysts and trap technologies to work efficiently, and to avoid pollution breakthrough, an effective feedback control loop is needed to manage the regeneration cycle of the NOx traps. To develop such control technology, there is an ongoing need for an economically-produced and reliable commercial ammonia sensor.
A need also exists for a reliable ammonia sensor for air ammonia monitoring in agricultural plants where ammonia present in animal shades, and in all other industries wherein ammonia is produced or used or is a by-product. Commercially available sensors typically suffer from lack of high sensitivity and selectivity. Thus, a widespread need exists for an improved ammonia gas sensor.